    Patent Literature 1: JP4618133B    Patent Literature 2: JP4665869B
Patent Literatures 1 and 2 disclose electromagnetic oil control valves (hereinafter referred to as OCV) for a pressurized oil circuit for a variable valve timing mechanism (hereinafter referred to as VVT) for an internal combustion engine (hereinafter referred to as ICE.) OCV is operated to control oil supply to and oil discharge from an advancing chamber and a retarding chamber which are disposed in an actuator for VVT.
OCV is an electromagnetic valve that has a spool valve and an electromagnetic actuator which are axially connected on an axial direction. The spool valve has a cylindrical sleeve and a spool supported within an internal bore of the sleeve in a reciprocally movable manner. The sleeve is formed with IN and OUT ports for oil. The spool changes communications between the IN and OUT ports by controlled to move in an axial direction to change axial location. The internal bore may also be referred to as a guide bore extending along a direction of a central axis. The electromagnetic actuator operates the spool by pushing the spool in a one direction of central axis directions along a central axis, and may also be referred to as a solenoid.
The internal bore of the sleeve is a guide bore for the spool. The guide bore extends straight along the central axis toward a distal end, which is an opposite end to the solenoid, from a base end, which is operatively connected with the solenoid. A return spring, which urges and pushes the spool in the other direction along the central axis, is disposed at a distal end portion within the internal bore of the sleeve.
The solenoid has a plunger, a solenoid coil, an inner stator core, an outer stator core and a connector. The plunger is a movable core, which is made of magnetic material and is connected with the spool via a shaft made of nonmagnetic material in order to be able to move as a single member. The solenoid coil generates magnetic flux and is referred to as a coil. The inner stator core is located radial inside of the coil and provides a magnetic path at the inside of the coil. The outer stator core is located radial outside of the coil and provides a magnetic path on the outside of the coil. The connector provides external electric connection between the coil and an external circuit.
The solenoid is configured to move the spool in the one direction along the central axis toward a full-lifted position on the distal end side from a zero-lifted position on the base end side of the sleeve by attracting the plunger to a magnetic attracting portion on the stator core by using magnetic force generated by the coil. In a case that it is required to reciprocally move the plunger smooth when the solenoid is activated, it is necessary to allow volumetric change on chambers located on both axial ends of the plunger. However, the solenoid is disposed on the cylinder head of the engine in externally exposed condition. Therefore, it is impossible to open the chambers to the air, since it is necessary to prevent oil from leaking outside of the engine.
To address the above-mentioned problem, the following structure may be employed. In this structure, a cup guide formed in a cylindrical shape with one bottom is disposed between an inside of the solenoid, i.e., a radial inside of the stator core and a radial outside of the plunger. In this structure, volumetric change of the chambers may be enabled by communicating the chambers to an inside of the spool bore. The chambers include a back chamber located on a back side of the plunger and a front chamber located on a front side of the chamber. The back chamber may be referred to as a first variable portion. The front chamber may be referred to as a second variable portion.
One known electromagnetic valve is configured to supply oil as lubricant to a slide clearance between the cup guide and the plunger, since the plunger is supported in a guide hole formed on the cup guide in a reciprocally slidable manner.
In addition, Patent Literature 1 discloses OCV which is configured to supply oil to the slide clearance by sucking oil up by using volumetric change, i.e., a suck and discharge action of the chamber on either ends of the plunger. The chamber is communicated to a sub-drain port which is formed on the base end side of the sleeve. However, this OCV may suck foreign matters with oil through the sub-drain port. In a case that if a foreign matter enters into the slide clearance, the cup guide or the plunger may not slide smooth or may create an unexpected amount of abrasion.
Patent Literature 2 discloses an OCV in which the sub-drain port is not formed and the above-mentioned problem is reduced. However, in the case of OCV in Patent Literature 2, if OCV is mounted on an engine with a substantially vertical arrangement, OCV cannot suck sufficient oil up to the solenoid from an axial inner bore of the spool. For example, OCV may be mounted to place the solenoid above than the spool and to arrange an axis of OCV in 60 or more angular degrees with respect to the horizontal plane. In such vertical arrangements, it becomes difficult to supply oil to reach a solenoid portion which is located in the cup guide and needs lubrication. Therefore, the cup guide or the plunger may not slide smooth due to insufficient amount of oil.